(1) Field of the Invention
The present invention relates to taps for mixing hot and cold water in sanitary facilities (wash-basins, showers, bathtubs, etc.), and in particular to a cartridge mixing valve provided with a thermostatic device suitable to maintain a constant water temperature.
(2) Description of Related Art
It is known that conventional single-control mixing taps include, a tap body with a cartridge mixing valve (hereinafter simply valve) removably inserted therein and a control lever for controlling a valve group, within the cartridge, made up of a pair of ceramic disks which adjust the flow of hot and cold water. This adjustment of the water, both in flow rate and in temperature, is carried out through the translation and rotation, respectively, of a mobile disk over an underlying fixed disk. In this way, the extent of aperture of the ports formed in said disks for the passage of hot and cold water is changed, and so is the ratio between hot water and cold water when they are mixed prior to the conveying to the tap mouth.
In order to maintain a constant temperature of the delivered water, both between two tap openings and during a same opening, it is possible to incorporate a thermostatic device in a conventional tap. Such a device acts downstream from the valve group by controlling the inflow of hot and cold water into the mixing chamber through respective ports.
As it will be better explained further on, this control is carried out automatically by a thermosensitive bulb which causes the shifting of a slider suitable to change the aperture of said ports in the mixing chamber. However, although known from some time, conventional thermostatic mixing valves still have some drawbacks of various nature.
A first drawback is the asymmetric thermal expansion that occurs when only hot water is delivered. In fact the metallic members of the thermostatic device are passed through by hot water coming from one side only, whereby they expand more on one side and tend to warp. As a result they may not work properly, for example the slider may get stuck and thus affect the operation of the device.
A second kind of drawback comes from the calcareous encrustations, especially on the hot water side, which may jeopardize the correct operation of the device. This problem stems from the fact that the slider travel is of a few tenths of a millimeter (usually max. 0.6 mm), therefore even small-size impurities may prove detrimental.
Still another kind of drawback is the use of a single control for temperature and flow rate, that implies a difficult repeatability of temperature between two openings. Moreover, there is a poor precision in adjusting the temperature due to the limited travel of the single control, which generally has a maximum rotatory travel of 90° around the tap mouth (±45°).
A known solution allowing to separate the flow rate control from the temperature control is to place the thermostatic device above the valve group. The use of two separate controls allows to achieve a more precise adjustment of temperature through the rotation of a ring along a greater arc (up to 360°), and also without any problem of repeatability between two openings.
However, even this solution is not free from drawbacks in that the flow rate control is a horizontal rotating lever located above the ring for the temperature adjustment. This still implies a position of the flow rate control higher than in conventional taps, which results in a tap having a greater overall height. Moreover, the above-described arrangement makes it difficult to reach the ring for the temperature adjustment, since the user has to insert his hand between the tap mouth and the lever above.
Secondly, the thermostatic device is located between the flow rate control and the valve group controlled by the latter. As a result, the flow rate adjustment is necessarily transmitted by a connection which passes through the thermostatic device, which is possibly used directly as a transmission means. In any case, the more or less close coupling between the flow rate control and the temperature control leads to a mutual interference which may affect the device operation. In other words, when changing the flow rate it may happen that also the temperature is changed and vice versa. Moreover, the thermostatic device is stressed also by loads not depending on its specific operation.
Therefore the object of the present invention is to provide a thermostatic mixing valve suitable to overcome the above-mentioned drawbacks.
This object is achieved by means of a valve in which the access path of the hot water to the mixing chamber is completely formed within a bottom base and the two ceramic disks of the valve group.